Discrepancy between process and memory information in crashdump

[Anshul Mittal]

In that case, won't the memory reported in the "Memory" tab also be
lesser (post garbage collection)?

Cheers,
Anshul Mittal


On Thu, Aug 13, 2020 at 7:34 AM Fred Hebert <mononcqc@REDACTED> wrote:

> From what I recall seeing, the crash dump, before being produced, has what
> looks like garbage collection running to eliminate some of the stale data.
>
> So if the node runs out of memory because it has a lot of garbage, you
> unfortunately can't see post-facto, and you have to kind of catch it live
> to analyze what is going on.
>
> Regards,
> Fred.
>
> On Thu, Aug 13, 2020 at 12:40 AM Anshul Mittal <mittal.anshul@REDACTED>
> wrote:
>
>> Hi,
>> I have a prod BEAM running on OTP 22 . I recently saw a crash in prod,
>> which generated a crash dump. The memory consumption of the process jumped
>> rapidly from ~5G to ~40G within a matter of a couple of minutes.
>>
>> Slogan: eheap_alloc: Cannot allocate 6664208 bytes of memory (of type
>> "old_heap").
>> System version: Erlang/OTP 22 [erts-10.7.1] [source-471fe20989] [64-bit]
>> [smp:36:36] [ds:36:36:10] [async-threads:1] [frame-pointer]
>>
>> When I analyzed the crash dump in the crash dump viewer, it shows the
>> following summary on the memory tab:
>>
>> Total: 50 GB
>> Processes: 42 GB
>> Processes Used: 42 GB
>> System: 7728 MB
>> ...
>>
>> However, when I sum the "Memory: " information from the individual
>> process entries in the crash dump, it only adds up to ~3G .
>>
>> I do see some processes with "WARNING: This process has an incomplete
>> heap. Some information might be missing. " However, from what I can tell
>> from the code here: https://fburl.com/ye99sjs9 , this warning means that
>> reference counted binaries are missing from the crash dump, and not the
>> information about the process heap itself.
>>
>> The crashdump itself doesn't seem to be truncated (don't see any such
>> message on the "General Information" tab in the viewer).
>>
>> What could explain the discrepancy here?
>>
>>
>> Cheers,
>> Anshul Mittal
>>
>
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